When a control device is connected to a peripheral device, there are a serial bus system in which peripheral devices (peripheral equipment) 1, 2 are connected to a control device 100 in a string as shown in FIG. 19(a) (for example, see Patent Document 1), and a parallel bus system in which wiring is branched to connect the peripheral devices 1, 2 as shown in FIG. 19(b) (for example, see Patent Document 2). In this connection, FIG. 19(a) and FIG. 19(b) each illustrate an example of two bus lines.
In the serial bus system as illustrated in FIG. 19(a), a connection in a string is provided such that the peripheral device 1 is connected to the control device 100, and that the peripheral device 2 are connected to the peripheral device 1. In this system, each of the peripheral devices sets in itself an ID number provided to the data received from the previous peripheral device (or the control device), and also updates and transmits the ID number for the next peripheral device. Therefore, the peripheral device can identifies its own attachment position, such that the peripheral device connected to the control device 100 is identified as the peripheral device 1 at an attachment position P1, the peripheral device connected to the peripheral device 1 at the attachment position P1 is identified as the peripheral device 2 at an attachment position P2, and the peripheral device that is connected to the peripheral device 2 at the attachment position P2 but is different from the peripheral device 1 at the attachment position P1 is identified as the peripheral device at an attachment position P3 (not shown). Thus, it is possible for the peripheral devices having the identical specification to be available, and the peripheral devices can be connected without checks of the attachment positions.
However, the serial bus system cannot be connected to the next peripheral device without going through a certain peripheral device and therefore a wiring loss such as redundancy of a wiring part going to and returning from the peripheral device arises as compared with the parallel bus system. Further, since the serial bus system has the peripheral devices each having an input terminal and an output terminal separately, it needs to have terminals twice as many as those of a parallel bus system that can combine them as an input/output terminal, resulting in an increased cost. In addition, the wirings of the peripheral devices are connected in a string; thus, when a partial disconnection thereof occurs, the subsequent peripheral devices become unable to communicate. For a countermeasure for the disconnection, there is a method such that the final peripheral device may be connected to the control device, which further leads to the wiring loss.
On the other hand, in the parallel bus system as shown in FIG. 19(b), a branching is carried out on a wiring without going through a peripheral device, and therefore a connection thereof is possible with the shortest wiring. In addition, the connection terminals for the peripheral device can be achieved with a minimum number of terminals to communicate with the control device.
However, when peripheral devices with an identical specification are connected in the parallel bus system, the peripheral devices are connected to the control device under electrically identical conditions, and therefore the control device is unable to recognize which peripheral device is connected to which attachment position.